>do not roll your own crypto
I believe this refers only to inventing your own algorithm, just
writing your own implementation of existing and tested algorithms is
fine.
Though, is encrypted root partition even desirable?
Since it only keeps your data safe when your machine is powered off, I
always
buzzard.2 is a classic: https://www.ioccc.org/years.html#1992
Despite being an entry to a competition, the code itself is actually
barely obfuscated, just very terse, and it comes with pretty good
design docs.
Stack machines and forth are rather good in general. I started by
reading https://users.